Heat Exchangers with Turbulizers Having Convolutions of Varied Height

ABSTRACT

A heat exchanger comprises at least one tube or plate pair defining a fluid flow passage which is reduced in height across a portion of its width. A turbulizer comprising a plurality of rows of convolutions is received inside the fluid flow passage in either the low pressure drop or high pressure drop orientation. The turbulizer includes convolutions of reduced height in order to at least partially fill the reduced-height portions of the fluid flow passage and thereby reduce bypass flow. In some preferred embodiments of the invention, heat exchanger tubes or plate pairs define fluid flow passages which are reduced in height along their edges, and the turbulizer is similarly reduced in height along its edges.

REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of application Ser. No. 11/119,222filed Apr. 29, 2005, the disclosure of which is incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to heat exchangers and conductive inserts for usetherein, and particularly to plate-type heat exchangers incorporatingturbulizers having convolutions of varying height.

BACKGROUND OF THE INVENTION

Plate-type heat exchangers comprise at least one pair of spaced-apartplates sealed together at their margins. Each plate pair defines a fluidflow passage having an inlet opening and an outlet opening. In a typicalheat exchanger, the edges of the fluid flow passage have a height whichis less than the height at the center of the fluid flow passage. Thereduction in height adjacent the edges may be due to the manner in whichthe plates are joined together and/or the edges of the plates may besomewhat rounded as in U.S. Pat. No. 5,636,685 to Gawve et al.

The fluid flow passage may contain a conductive insert to enhance heattransfer and to increase turbulence in the fluid flowing through theflow passage. These conductive inserts, which are also known asturbulizers, usually comprise strips of metal in which a plurality ofconvolutions are formed by stamping and/or rolling. The convolutions areusually of a uniform height and are preferably in contact with bothplates of the plate pair to maximize heat transfer. Numerous types ofturbulizers are known in the prior art. One type of turbulizer which maybe used in vehicular oil coolers is the louvered fin described in U.S.Pat. No. 4,945,981 (Joshi) issued on Aug. 7, 1990. Another type ofturbulizer for use in vehicular heat exchangers is the offset strip fin,examples of which are described in U.S. Pat. No. Re. 35,890 (So) andU.S. Pat. No. 6,273,183 (So et al.). The patents to So and So et al. areincorporated herein by reference in their entireties.

As illustrated in FIGS. 1 to 3 of Gawve et al., a turbulizer of constantheight cannot fill the entire area of a fluid flow passage which isreduced in height adjacent its edges, while maintaining effectivecontact with the plates. This causes the formation of a fluid bypass B(FIG. 3 of Gawve et al.) adjacent the edges of the fluid flow passage,which lowers the efficiency of heat transfer. This problem is partiallysolved in Gawve et al. by indenting the fin walls to reduce their heightadjacent their ends, thereby reducing the bypass area B′ as shown inFIG. 7.

While the Gawve et al. patent addresses the problem of bypass flow, itis specific to corrugated fins extending transverse to the direction offluid flow and having fin walls which extend across the entire width ofthe turbulizer. There remains a need to address the problem of bypassflow in heat exchangers using other types of turbulizers, such as theoffset strip fins mentioned above.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises a heat exchanger comprising: (a)at least one pair of plates which are joined together to define a hollowfluid flow passage between the plates, wherein the flow passage has aheight and a width and extends along a fluid flow axis, wherein theheight of the flow passage varies across its width, wherein the flowpassage comprises at least one full-height area in which the height ofthe flow passage is at a maximum and at least one reduced-height area inwhich the height of the flow passage is less than the maximum height ofthe flow passage, and wherein the full-height and reduced-height areasare located adjacent to one another; (b) a turbulizer received insidethe fluid flow passage, wherein the turbulizer comprises a plurality ofconvolutions arranged in at least one row, wherein the convolutions ofeach said row comprise a series of crests and troughs interconnected byside walls, and wherein the rows extend transverse to the fluid flowaxis and the side walls extend along the fluid flow axis; wherein eachof the rows includes convolutions of different heights, including atleast one full-height convolution positioned in the full-height area ofthe fluid flow passage and having a height substantially the same as themaximum height of the flow passage, and including at least onereduced-height convolution positioned in the reduced-height area of thefluid flow passage and having a height which is less than the maximumheight of the flow passage.

In another aspect, the invention comprises a heat exchanger comprising:(a) at least one pair of plates which are joined together to define ahollow fluid flow passage between the plates, wherein the flow passagehas a height and a width and extends along a fluid flow axis, whereinthe height of the flow passage varies across its width, wherein the flowpassage comprises at least one full-height area in which the height ofthe flow passage is at a maximum and at least one reduced-height area inwhich the height of the flow passage is less than the maximum height ofthe flow passage, and wherein the full-height and reduced-height areasare located adjacent to one another; (b) a turbulizer received insidethe fluid flow passage, wherein the turbulizer comprises a plurality ofrows of convolutions, wherein adjacent ones of said rows are connectedin side-by-side parallel relation to one another, wherein theconvolutions of each said row comprise a series of crests and troughsinterconnected by side walls, and wherein the rows extend parallel tothe fluid flow axis and the side walls extend transverse to the fluidflow axis; wherein at least two adjacent rows are comprised ofconvolutions of different heights, including at least one row offull-height convolutions positioned in the full-height area of the fluidflow passage and having a height substantially the same as the maximumheight of the flow passage, and including at least one row ofreduced-height convolutions positioned in the reduced-height area of thefluid flow passage and having a height which is less than the maximumheight of the flow passage.

In yet another aspect, the present invention provides a heat exchangercomprising: (a) at least one heat exchange tube defining a hollow fluidflow passage, wherein the flow passage has a height and a width andextends longitudinally along a fluid flow axis, wherein the height ofthe flow passage varies across its width, wherein the flow passagecomprises at least one full-height area in which the height of the flowpassage is at a maximum and at least one reduced-height area in whichthe height of the flow passage is less than the maximum height of theflow passage, and wherein the full-height and reduced-height areas arelocated adjacent to one another; (b) a turbulizer received inside thefluid flow passage; wherein each said heat exchange tube comprises anelongate upper plate and an elongate lower plate in sealed engagementwith one another; wherein the upper plate comprises a longitudinallyextending central portion and a pair of longitudinally extending edgeportions provided along either side of the central portion, the centralportion being raised relative to the edge portions; wherein the lowerplate comprises a longitudinally extending central portion locatedopposite the upper plate; a pair of longitudinally extending edgeportions extending from the central portion of the lower plate in adirection toward the upper plate, wherein the edge portions of the lowerplate each have a proximal edge joined to the central portion of thelower plate and a distal edge proximate to one of the edge portions ofthe upper plate; and a pair of locking tabs, each of which extends fromthe distal edge of one of the lower plate end portions; wherein thelocking tabs of the lower plate are folded into engagement over the edgeportions of the upper plate and the plates are sealed together alongareas of contact between the locking tabs and the edge portions of theupper plate.

In yet another aspect, the present invention provides a heat exchangercomprising: (a) at least one heat exchange tube defining a hollow fluidflow passage and having a top wall, a bottom wall and a pair of sidewalls, wherein the flow passage has a height and a width and extendslongitudinally along a fluid flow axis, wherein the height of the flowpassage varies across its width, wherein the flow passage comprises atleast one full-height area in which the height of the flow passage is ata maximum and at least one reduced-height area in which the height ofthe flow passage is less than the maximum height of the flow passage,and wherein the full-height and reduced-height areas are locatedadjacent to one another; (b) a turbulizer received inside the fluid flowpassage) wherein each said heat exchange tube comprises a pair ofgenerally U-shaped sections, each having a bight portion and a pair oflegs extending from the bight portion, wherein the bight portions formthe side walls of the tube and the legs form the top and bottom walls ofthe tube; wherein the legs of each U-shaped section have free andportions, each of the end portions of a first one of the U-shapedsections being in sealed engagement with one of the and portions of asecond one of the U-shaped sections, such that the top and bottom wallsof the tube are each formed by one of the legs of the first U-shapedsection and one of the legs of the second U-shaped section.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional perspective view of a plate pair providedwith a prior art turbulizer;

FIG. 2 is a perspective view of a portion of the turbulizer shown inFIG. 1;

FIG. 3 is a front view of the turbulizer of FIG. 1, showing the relativeorientations of overlapping convolutions in two adjacent rows;

FIG. 4 is a cross-sectional perspective view of a plate pair providedwith a turbulizer according to a preferred embodiment of the invention;

FIG. 4A is a cross-sectional perspective view of a modified version ofthe plate pair of FIG. 4;

FIG. 5 is a perspective view of a portion of the turbulizer shown inFIG. 4;

FIG. 6 is a front view of the turbulizer of FIG. 5, showing the relativeorientations of overlapping convolutions in two adjacent rows;

FIG. 7 is a front view of a first variant of the turbulizer of FIGS. 5and 6, showing the relative orientations of overlapping convolutions intwo adjacent rows;

FIG. 8 is a front view of a second variant of the turbulizer of FIGS. 5and 6, showing the relative orientations of overlapping convolutions intwo adjacent rows;

FIG. 9 is a cross-sectional perspective view of a plate pair providedwith a turbulizer according to another preferred embodiment of theinvention;

FIG. 10 is a front view of the turbulizer of FIG. 9, showing therelative orientations of overlapping convolutions in two adjacent rows;

FIG. 11 is a perspective view of a portion of a turbulizer according toanother preferred embodiment of the invention;

FIG. 12 is a cross sectional side view of one row of the turbulizer ofFIG. 11, taken along line 12-12 of FIG. 11;

FIG. 13 is a cross sectional side view of one row of the turbulizer ofFIG. 11, taken along line 13-13 of FIG. 11;

FIG. 14 is a cross sectional end view through a first plate pairincluding the turbulizer strip of FIGS. 11 to 13;

FIG. 15 is a cross sectional end view through a second plate pairincluding the turbulizer strip of FIGS. 11 to 13;

FIG. 16 is a cross sectional end view through a third plate pairincluding the turbulizer strip of FIGS. 11 to 13; and

FIG. 17 is a perspective view of a portion of a turbulizer stripaccording to another preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following is a description of a number of preferred heat exchangers,plate pairs and turbulizer strips according to the invention. Each heatexchanger described below comprises a pair of plates defining a fluidflow passage. The heat exchangers according to the invention maycomprise a single pair of plates, for example as in the oil coolersdescribed by Joshi and Gawve et al. Alternatively, the heat exchangersaccording to the invention may comprise a plurality of plate pairsextending between a pair of manifolds, such as the type described in theSo et al. patent. In the heat exchangers according to the invention, aturbulizer is provided in the fluid flow passage. Unless otherwisestated below, the turbulizers used in the heat exchangers according tothe invention may be simple corrugated fins as in the Joshi and Gawve etal. patents or may comprise offset strip fins as described in the So andSo et al. patents mentioned above. Preferably, the turbulizers compriseoffset strip fins.

Throughout the following description and claims, terms such as “top”,“bottom”, “upper” and “lower” are used to refer to the specificorientation of the plate pairs and turbulizers. It will be appreciatedthat these terms are used for convenience only. The tops and bottoms ofthe turbulizers are preferably indistinguishable from each other and theplate pairs do not necessarily have the orientation shown in thedrawings when in use.

Problems associated with the prior art are now discussed below withreference to FIG. 1, showing a portion of a plate pair 61 of a heatexchanger provided with a prior art turbulizer 33 having convolutions ofconstant height, and with reference to FIGS. 2 and 3 which show theprior art turbulizer 33 in isolation.

The plate pair 61 is comprised of an upper plate 62 and a lower plate63, with a turbulizer 33 located therebetween. Plates 62, 63 arearranged back-to-back and have joined peripheral flanges 64, 65. Plates62, 63 also have raised central portions 66, 67 which define a flowpassage 68 therebetween in which the turbulizer 33 is located.

It will be seen that the plates 62, 63 making up plate pair 61 arerounded adjacent to the peripheral flanges 64, 65 and therefore the flowpassage 68 is reduced in height along its edges 69, 71.

The turbulizer 33 shown in FIGS. 1 to 3 is an offset strip fin similarto that shown in above-mentioned patent '890 to So. Turbulizer 33 is aplanar member comprising a plurality of rectangular shaped convolutions35 disposed in transverse rows shown at 47, 49, 51, 53 and 55. The rowsare joined to one another through connecting portions 43. A completeturbulizer 33 would include a number of additional rows of convolutions.The convolutions 35 comprise a top surface portion 36, a bottom surfaceportion 37 (portions 36 and 37 are also referred to herein as “crests”),and side portions 38 which interconnect the top and bottom surfaceportions 36, 37. Convolutions 35 define apertures or flow passageways 39opening in a direction transverse to the direction of rows 47, 49, 51,53, 55. When a fluid such as oil flows through the flow passage 68defined by plate pair 61, it will periodically encounter leading edges41 associated with convolutions 35.

All the convolutions 35 of turbulizer 33 are of the same height H andthe same width W (FIG. 3), the width being defined as the width of thetop and bottom portions 36, 37 of corrugations 35. In order to maximizeheat transfer, the top and bottom portions 36, 37 of corrugations 35 arepreferably in contact with the central portions 66, 67 of the upper andlower plates 62, 63. The turbulizer 33 is arranged in the “low pressuredrop” or “LPD” orientation, meaning that fluid flows through theopenings defined by the convolutions, in a direction transverse to therows. In this orientation, the fluid passing through the flow passage 68encounters relatively little resistance to flow and therefore thepressure drop is relatively low.

As shown in FIG. 1, the turbulizer 33 is of a constant height which issubstantially the same as the height of the flow passage 68 between thecentral portions 66, 67 of plates 62, 63. It is not possible to extendthe turbulizer 33 to the edges 69, 71 of the flow passage 68 because theedges 69, 71 are reduced in height. Therefore the turbulizer 33 will notfit within these areas, at least not without being crushed. This causesthe formation of bypass areas 40, 42 which are coincident with the edges69, 71 of the flow passage 32. The resistance to fluid flow is at aminimum in these bypass areas 40, 42. Therefore, fluid preferentiallyflows through these areas and the efficiency of heat transfer isreduced.

FIG. 4 illustrates a portion of a plate pair 44 for use in a heatexchanger according to a first preferred embodiment of the invention,and FIGS. 5 to 8 illustrate preferred turbulizers according to theinvention. Plate pair 44 comprises an elongate upper plate 12 and anelongate lower plate 14. The upper plate 12 has a central portion 16extending along longitudinal axis L and edge portions 18 and 20extending longitudinally along either side of the central portion 16.The central portion 16 is raised relative to the edge portions 18 and20, for reasons which will be discussed below.

The lower plate 14 comprises a longitudinal central portion 22 andcomprises longitudinal edge portions 24 and 26 projecting at anapproximately right angle from central portion 22, thereby forming sidewalls of the plate pair 44. The edge portions 24 and 26 are providedwith locking tabs 28 and 30 which are bent down into locking engagementover the edge portions 18 and 20 of the upper plate 12. The tabs 28 and30 mechanically lock the plates 12 and 14 together (as better shown inFIG. 4A) and provide surfaces along which a sealed connection can bemade with the edge portions 18 and 20 of the upper plate. A sealedconnection may preferably be provided by brazing the upper and lowerplates 12 and 14 together so that a fillet of braze filler metal (notshown) is formed between the locking tabs 28 and 30 of lower plate 14and the edge portions 18 and 20 of upper plate 12.

As shown in FIG. 4, the central portion 16 of upper plate 12 is raisedrelative to the edge portions 18 and 20 so that the locking tabs 28 and30 of lower plate 14 are approximately coplanar with the central portion16 of upper plate 12. This provides the plate pair 44 with asubstantially flat upper surface which is free of projections. This isadvantageous, for example where the ends of the plate pair 44 must fitinto a rectangular slot of a header plate (not shown). Since the edgeportions 18 and 20 are recessed relative to the central portion 16, thefluid flow passage 32 formed by the plate pair 44 is relatively higherin the middle than at its edges.

FIG. 4A illustrates a plate pair 44′ which is a modified version ofplate pair 44 described above. Plate pair 44′ includes an upper plate12′ having a central portion 16′ extending along longitudinal axis L andedge portions 18′ and 20′ extending longitudinally along either side ofthe central portion 16′. The central portion 16′ is raised relative tothe edge portions 18′ and 20′. The edge portions 18′ and 20′ areprovided with downward extensions 17, 19 extending at an approximatelyright angle from the edge portions 18′, 20′ and preferably extendinglongitudinally along the entire length of upper plate 12′.

Plate pair 44′ also includes a lower plate 14 which is identical to thatof plate pair 44, having a central portion 22 and edge portions 24, 26projecting at an approximately right angle from central portion 22,thereby forming side walls of the plate pair 44′. The edge portions 24,26 are provided with locking tabs 28, 30 which, as shown in dotted linesin FIG. 4A, are initially upstanding and coplanar with the edge portions24, 26, but which are bent downwardly in the direction of the curvedarrows into engagement with the edge portions 18′, 20′ of the upperplate 12′. As shown in FIG. 4A, the downward extensions 17, 19 are ofsufficient height such that their lower free ends (distal to the edgeportions 18′, 20′) make contact with the central portion 22 of the lowerplate 14 and are nested in parallel relation with the edge portions 24,26 of the lower plate 14. The downward extensions 17, 19 provide theplate pair 44′ with a double edge wall thickness for increased strength;provide increased surface area for braze joints; facilitate assembly bypermitting the turbulizer to be inserted into one of the plates prior toassembly of the plate pair; and provide support for the edge portions24, 26 of the lower plate 14 during the forming/locking operation.

The plate pairs 44 and 44′ of FIGS. 4 and 4A each define a fluid flowpassage 46, 46A in which a turbulizer 48 is provided. The turbulizer 48is described below in relation to FIG. 4 only. The turbulizer 48comprises an offset strip fin similar to the strip fin 33 describedabove, having a plurality of rectangular shaped convolutions 50 disposedin a plurality of transverse rows shown at 75, 77, 79, 81, 83, 85, 87and 89 (FIG. 5). The rows are joined together through connectingportions 91. It will be appreciated that a complete turbulizer 48 wouldalso include a number of additional rows of convolutions 50.

The convolutions 50 comprise flat top surface portions 52, flat bottomsurface portions 54 and vertical side portions 56 which interconnect thetop and bottom surface portions 52, 54. Convolutions 50 define aperturesor flow passageways 93 opening in a direction transverse to thedirection of the rows. When a fluid such as oil flows through the flowpassage 46 defined by plate pair 44, it will periodically encounterleading edges 95 associated with convolutions 50.

The turbulizer 48 includes convolutions 50 of varying height. Morespecifically, each row includes a first plurality of convolutions 50 ofwidth W and height H, wherein height H is substantially the same as theheight of the flow passage 46 between the central portion 16 of upperplate 12 and the central portion 22 of lower plate 14. The convolutionsof height H are located inward of the ends of the rows, such that thetop and bottom surface portions 52, 54 of convolutions 50 make contactwith the central portions 16 and 22 of the upper and lower plates 12 and14.

Located at either end of each row is at least one convolution 50,labelled as 50A, having width W_(A) and height H_(A), wherein widthW_(A) is the same as width W and height H_(A) is less than height H.Furthermore, height H_(A) is substantially the same as the height of theflow passage 46 between the edge portions 18 and 20 of the upper plate12 and the central portion 22 of lower plate 14. These convolutions 50Aare comprised of top surface portions 52A, bottom surface portions 54Aand side portions 56A. In the preferred embodiment shown in FIGS. 4 to6, the side portions 56A are shorter than side portions 56 ofconvolutions 50, while the top and bottom surface portions 52A, 54A arethe same width as top and bottom surface portions 52, 54 of convolutions50. In addition, the bottom surface portions 54 and 54A are coplanarwhile the top surface portions 52A are reduced in height relative to topsurface portions 52 in order to conform to the shape of the flow passage46. Therefore, as shown in FIG. 4, the convolutions 50A occupy the areasreferred to as bypass areas 40 and 42 of FIG. 1, with the top surfaceportions 52A of convolutions 50A in contact with the edge portions 18,20 of upper plate 12, and with the bottom surface portions in contactwith the lower plate 14.

The turbulizer 48 shown in FIGS. 4 to 6 shows only one reduced-heightconvolution 50A at the end of each row. However, it will be appreciatedthat more than one reduced-height convolution 50A may be provided at oneor both ends of each row, depending on the configuration of the flowpassage and the width of the convolutions 50. It will also beappreciated the reduced-height convolutions 50A may preferably beprovided only at one end of turbulizer 48, depending on theconfiguration of the flow passage 46. It will also be appreciated thatthe reduced height convolutions at one end of the rows may differ inheight and/or width relative to the reduced height convolutions at theother end of the rows.

FIGS. 7 and 8 illustrate two variants of the turbulizer shown in FIGS. 4to 6, designed to fit flow passages of varying configuration, and likeelements of these turbulizers are identified by like reference numerals.FIG. 7 illustrates two rows 75, 77 of a turbulizer 58. Each rowcomprises a plurality of centrally-located convolutions 50 having heightH and width W. Located at either end of each row 75, 77 is at least oneconvolution 50B having width W_(B) which is the same as width W andheight H_(B) which is less than height H. The convolutions 50B have sideportions 56B which are shorter than side portions 56 of convolutions 50,and top and bottom surface portions 52B, 54B having the same width astop and bottom surface portions 52, 54 of convolutions 50. In addition,the top surface portions 52 and 52B are coplanar while the bottomsurface portions 54B are elevated relative to top surface portions 54.

FIG. 8 illustrates two rows 75, 77 of a turbulizer 60. Each rowcomprises a plurality of centrally-located convolutions 50 having heightH and width W. Located at either end of each row 75, 77 is at least oneconvolution 50C having width W_(C) which is less than width W and heightH_(C) which is less than height H. The convolutions 50C have sideportions 56C which are shorter than side portions 56 of convolutions 50,and top and bottom surface portions 52C, 54C which are narrower than topand bottom surface portions 52, 54 of convolutions 50. In addition, thetop surface portions 52C are reduced in height relative to top surfaceportions 52 while the bottom surface portions 54C are elevated relativeto bottom surface portions 54.

It will be appreciated that turbulizers 48 and 58 of FIGS. 6 and 7 couldbe modified by increasing or decreasing the widths of the top surfaceportions 52A, 52B and/or the widths of the bottom surface portions 54A,54B thereof, thereby varying the pitch as well as the height of theconvolutions 50A, 50B along the longitudinally extending edges ofturbulizers 48, 58. It will also be appreciated that turbulizer 60 ofFIG. 8 could be modified by either making the width of top surfaceportions 52C and/or bottom surface portions 54C the same as or greaterthan the width of top and bottom surface portions 52, 54.

It will be appreciated that the turbulizers 48 and 58 shown in FIGS. 6and 7 are particularly useful where only one of the top or bottom wallof the plate pair converges toward the opposing top or bottom wall ofthe plate pair adjacent to the edges of the plate pair, as in FIG. 4. Onthe other hand, the turbulizer 60 shown in FIG. 8 is particularly usefulwhere both the top and bottom walls of the plate pair converge towardone another adjacent to the edges of the plate pair, as in FIG. 1.

FIG. 9 illustrates a portion of another preferred plate pair 70according to the invention, incorporating a turbulizer 94, and FIG. 10illustrates a portion of turbulizer 94 in isolation. Plate pair 70 isconstructed from first and second U-shaped plates 72 and 74. The firstU-shaped plate 72 has a pair of straight parallel side portions 76 and78 (also referred to herein as “legs”) joined by a curved portion 80(also referred to herein as a “bight portion”). The second U-shapedplate 74 similarly has substantially straight, parallel side portions 82and 84 joined by a curved portion 86. The side portions 82 and 84 of thesecond U-shaped plate 74 are provided with shoulders 88 and 90 whichengage the inner surfaces of side portions 76 and 78 of the firstU-shaped plate 72. The engagement of shoulders 88 and 90 with the sideportions 76 and 78 provides a mechanical connection between the plates72 and 74 and also provides surfaces along which the plates 72 and 74can be joined, for example by brazing.

It will be appreciated that both shoulders 88 and 90 are not necessarilyprovided on same U-shaped plate section, but rather each U-shaped platesection may be provided with one shoulder on one of its side portions.

The plate pair 70 defines a fluid flow passage 92 in which a turbulizer94 is provided. The turbulizer 94 comprises an offset strip fin similarto strip fins 33, 48, 58 and 60 described above. Turbulizer 94 comprisesa plurality of convolutions 96 disposed in a plurality of transverserows, of which only two rows 97, 99 are shown in FIGS. 9 and 10. Theconvolutions 96 comprise top surface portions 98 and bottom surfaceportions 100 which are more rounded than the top and bottom surfaceportions of the turbulizers described above, but which have flatportions for engaging the side portions 76, 78, 82, 84 of the plates 72,74. The convolutions 96 further comprise side portions 102 whichinterconnect the top and bottom surface portions 98, 100. In turbulizer94 the side portions 102 are sloped rather than vertical as in theturbulizers described above. It will be appreciated that theconvolutions 96 of turbulizer 94 do not necessarily have the shape shownin FIGS. 9 and 10, but may have an alternate shape. For example, theymay be rectangular as in the turbulizers described above.

Convolutions 96 define apertures or flow passageways 101 opening in adirection transverse to the direction of the rows 97, 99. When a fluidsuch as oil flows through the flow passage 46 defined by plate pair 44,it will periodically encounter leading edges 103 associated withconvolutions 96.

The turbulizer 94 includes convolutions 96 of varying height. Morespecifically, each row includes a first plurality of convolutions 96 ofwidth W and height H, wherein height H is substantially the same as themaximum height of the fluid flow passage 92 between the side walls ofthe plates 72 and 74.

The first plurality of convolutions 96 comprises two groups which areseparated by at least one convolution 96A having a width W_(A) the sameas height W and a height H_(A) which is less than height H. Height H_(A)is substantially the same as the height of the flow passage 94 at thepoint where the first and second U-shaped plates 72 and 74 are joined,i.e. between shoulders 88 and 90. The convolutions 96A comprise topsurface portions 98A, bottom surface portions 100A and side portions102A. In the preferred embodiment shown in the drawings, the sideportions 102A are shorter than side portions 102 of convolutions 96,while the top and bottom surface portions 98A, 100A are same width asthe top and bottom surface portions 98 of convolutions 96. In addition,the top surface portions 98A are reduced in height relative to the topsurface portions 98 while the bottom surface portions 100A are elevatedrelative to bottom surface portions 100.

Located at either end of each row 97, 99 is at least one convolution 96Bhaving a width W_(B) which is the same as width W and height H_(B) whichis less than heights H and H_(A). The convolutions 96B have sideportions 102B which are shorter than side portions 102 and 102A and havetop and bottom surface portions 98B, 100B which are the same with as topand bottom surface portions 98, 100. In addition, the bottom surfaceportions 100B and 100A are coplanar while the top surface portions 98Bare reduced in height relative to the top surface portions 98 and 98A ofconvolutions 96 and 96A. It will be appreciated that convolutions 96Bextend into the areas of reduced height adjacent to the edges of flowpassage 92.

In the embodiments of the invention described above, the turbulizers arepositioned in the fluid flow passages in the low pressure droporientation, i.e. with the rows of convolutions disposed transverse tothe flow direction and transverse to the longitudinal axis of the platepair. The present invention also includes embodiments in which theturbulizers are arranged in the high pressure drop orientation, in whichthe rows of convolutions are disposed parallel to the flow direction andparallel to the longitudinal axis of the plate pair. These embodimentsare now described below.

FIGS. 11 to 14 illustrate another preferred embodiment of the inventionutilizing a turbulizer 120 comprising a plurality of convolutions 124,134 disposed in rows 122 extending along longitudinal axis L, which isparallel to the direction of fluid flow.

A first plurality of rows 122, spaced from the longitudinal edges ofturbulizer 120, is comprised of generally sinusoidal-shaped convolutions124 having a first height H. Convolutions 124 comprise smoothly curvedtop and bottom surface portions 126, 127 connected by sloping sideportions 128. The sloping side portions 128 are interrupted at abouttheir midpoints by shoulders 130 through which adjacent rows 122 areconnected together. These shoulders 130 are interconnected to formcontinuous lines 132 extending transversely across the turbulizer 120.

The turbulizer 120 also includes a plurality of rows 122, labelled 122A,comprised of convolutions 134 which are of a somewhat reduced heightH_(A) relative to the convolutions 124. These rows 122A extend along thelongitudinal edges of the turbulizer 120. A cross sectional view througha portion of a row 122A of reduced height convolutions 134 is shown inFIG. 13. As shown, the convolutions 134 are comprised of flat top andbottom surface portions 136, 137 which are connected by sloping sideportions 138. The side portions 138 are interrupted by shoulders 140which are relatively wider than shoulders 130 of convolutions 124 andthrough which the convolutions 134 at the edges of the turbulizer strip120 are connected to convolutions 124 in neighbouring rows.

The convolutions 124, 134 define apertures or flow passageways 125 openin a direction transverse to the direction of rows 122 and transverse tothe flow direction. When a fluid such as oil flows through theturbulizer 120 by following a tortuous path through the transverseopenings between convolutions of adjacent rows 122, it will periodicallyencounter the side portions 128, 138 of the convolutions 124, 134. Thisorientation is referred to as the high pressure drop orientation.

FIG. 14 illustrates a turbulizer strip 120 located in the fluid flowpassage 142 of a plate pair 144 which is comprised of upper and lowerplates 146, 148 and is generally of the same shape as prior art platepair 61 shown in FIG. 1. The cross section of FIG. 14 is taken in atransverse plane through the continuous line 132 formed by the shouldersof the convolutions 124, 134. The plates 146, 148 are arrangedback-to-back and have joined peripheral flanges 152, 158. Plates 146,148 also have raised central portions 150, 156 which are connected toflanges 152, 158 through sloping, rounded side walls 154, 160. Due tothe presence of sloping, rounded side walls 154, 160, the fluid flowpassage 142 of plate pair 144 has a central portion having a heightwhich is equal to the distance between the central raised portions 150,156 of the plates 146 and 148. The area approaching the flanges 152, 158is gradually reduced in height.

As mentioned above, the turbulizer 120 is positioned in the fluid flowpassage 142 in the high pressure drop orientation. The rows 122 havingconvolutions 124 of height H are located between and in contact with thecentral raised portions 150, 156 of the plates 146, 148. The rows 122Aalong the edges of turbulizer strip 120 having convolutions 134 ofheight H_(A) are located adjacent the edges of the fluid flow passage142, i.e. adjacent to flanges 152, 158. In order to minimize the bypassarea adjacent the edges of the flow passage 142, it is preferred thatthe reduced height convolutions 134 make at least some contact with theupper and lower plates 146 and 148, as shown in FIG. 14. However, due tothe curved shape of the edges of flow passage 142 and the square shapeof the convolutions, it will be appreciated that complete contact withthe plates 146 and 148 is not possible.

FIGS. 15 and 16 show that the turbulizer 120 can be used in heatexchangers formed from flat, extruded tubes of varying shapes, ratherthan the plate pairs described above. The cross sections of FIGS. 15 and16 are taken in a transverse plane through the top and bottom surfaceportions of convolutions 124, 134.

In FIG. 15, the turbulizer 120 is disposed in the high pressure droporientation in a flat heat exchange tube 180 having flat, parallel topand bottom walls 182, 184 and substantially vertical side walls 186,188. Together, the walls 182, 184, 186, 188 define a fluid flow passage190. The top, bottom and side walls are connected together by angledtransitions 192, 194, 196 and 198 which reduce the height of the flowpassage 190 adjacent to its outer edges. It will be seen that thereduced height convolutions 134 of turbulizer 120 fill a large portionof the area located between angled transitions 192 and 194 and the arealocated between angled transitions 196 and 198, thereby substantiallyreducing bypass flow through the tube 180.

In FIG. 16, the turbulizer 120 is disposed in the high pressure droporientation in a flat heat exchange tube 200 having flat, parallel topand bottom walls 202, 204 connected by rounded side portions 206, 208.Together, the walls 202, 204 and side portions 206, 208 define a fluidflow passage 210. The height of the flow passage 210 is reduced withinthe rounded side portions 206, 208. It will be seen that the reducedheight convolutions 134 of turbulizer 120 fill a large portion of thearea located within the rounded side portions 206, 208, therebysubstantially reducing bypass flow through the tube 200.

In the turbulizer 120 shown in FIGS. 11 to 13, the flat top portions 136of the reduced height convolutions 134 are reduced in height relative tothe top portions 126 of the full-height convolutions 124 and the flatbottom portions 137 of the reduced-height convolutions 134 are elevatedrelative to the bottom portions 127 of the full-height convolutions 124.Thus, the turbulizer 120 is particularly useful in heat exchange tubesor plate pairs such as those shown in FIGS. 14 to 16 in which the topand bottom walls of the tube or plate pair converge toward a centralplane.

It will however be appreciated that the turbulizer 120 could be modifiedfor use in a tube or plate pair similar or identical to those shown inFIGS. 4 and 4A where the bottom wall of the tube or plate pair is flatand the top wall of the tube or plate pair converges toward the bottomwall adjacent its edges. Specifically, the turbulizer 120 could bemodified so that the bottom portions 137 of the reduced-heightconvolutions 134 are coplanar with the bottom portions 127 of thefull-height convolutions 124. For example, the lower portions of thereduced height convolutions 134 (below shoulders 140) could have thesame or similar sinusoidal shape and height as the full heightconvolutions 124. This possibility is illustrated by dotted line portion123 in the cross section of FIG. 13.

FIG. 17 illustrates another preferred turbulizer 170 for use in heatexchangers according to the invention. Turbulizer 170 is similar in anumber of respects to turbulizer 120 shown in FIGS. 11 to 13, and likereference numerals are used to identify like components in theturbulizer of FIG. 17. Turbulizer 170 comprises a plurality of rows 122of convolutions. Some of these rows 122 are comprised of full heightconvolutions 124 which are spaced inwardly from the edges of theturbulizer strip 170. The turbulizer strip 170 also includes a number ofrows 122, labelled 122A, comprised of reduced height convolutions 134.Rows 122A are located along the longitudinally extending edges ofturbulizer strip 170. In the embodiment of FIG. 17, there is one row 122of reduced height convolutions 134 along each edge of the turbulizerstrip 170. The convolutions 124 and 134 of turbulizer strip 170 areexactly the same as in turbulizer 120 and therefore further discussionof these convolutions is not necessary. Turbulizer 170 is preferablydisposed in a plate pair or extruded heat exchanger tube in a highpressure drop orientation as shown in FIGS. 14 to 16, that is with rows122 extending transverse to the direction of fluid flow.

In addition, the turbulizer 170 of FIG. 17 is provided with spaced apartrows 172 which are comprised of reduced height convolutions 174. Rows172 are located between the rows of full height convolutions 122.Convolutions 174 may preferably have the same shape and dimensions asconvolutions 134 shown in FIG. 13, although this is not necessary. Therows 172 comprised of reduced height convolutions 174 provide pressurerecovery zones to avoid excessive pressure drop as the fluid flowsthrough the turbulizer 170 in the high pressure drop orientation.

Although the preferred plate pairs 44, 44′ and 70 shown in FIGS. 4, 4Aand 9 are shown in the drawings as being provided with turbulizersarranged in the low pressure drop orientation, it will be appreciatedthat these and similar plate configurations can be used in combinationwith turbulizers arranged in the high pressure drop orientation, such asthe turbulizers shown in FIGS. 11 to 13 and 17. For example, theturbulizer 170 shown in FIG. 17 could be used in a plate pair 70 asshown in FIG. 9. To fit within the flow passage of plate pair 70, theturbulizer 170 would be provided with at least one row 122 of reducedheight convolutions 134 along each of its edges and would be providedwith at least one row 172 of reduced height convolutions 174 to fitbetween the shoulders 88 and 90 formed in the overlapping end portionsof the U-shaped plates.

Although the invention has been described in connection with certainpreferred embodiments, it is not restricted thereto. Rather, theinvention includes all embodiments which may fall within the scope ofthe following claims.

1. A heat exchanger comprising: (a) at least one substantially flat heatexchange tube having top and bottom walls defining a hollow fluid flowpassage, wherein the fluid flow passage has a height, a width and alength, with the height defined between said top and bottom walls of thetube, and with the tube extending lengthwise along a fluid flow axis,wherein the height of the fluid flow passage varies across the width soas to define a full-height area with a first height and a reduced-heightarea with a second height, wherein the first height is equal to amaximum height of the fluid flow passage and is greater than the secondheight, and wherein both the full-height area and the reduced-heightarea extend along the fluid flow axis; (b) a turbulizer provided insidethe fluid flow passage, wherein the turbulizer has a height, a width anda length, with the turbulizer extending lengthwise along the fluid flowaxis and substantially completely filling the fluid flow passage,wherein the turbulizer comprises a plurality of rows of convolutionsconnected in side-by-side parallel relation to one another, and whereinthe convolutions of each said row comprise a series of top surfaceportions and bottom surface portions interconnected by side portions;wherein the convolutions are pre-formed in a manufacturing process,prior to being provided inside the fluid flow passage, so as to define aplurality of full-height convolutions having a height substantially thesame as the first height of the fluid flow passage, and a plurality ofreduced-height convolutions having a maximum height substantially thesame as the second height of the fluid flow passage, wherein the sideportions of the reduced-height convolutions are shorter than the sideportions of the full-height convolutions; and wherein the full-heightconvolutions and the reduced height convolutions are arranged such thatone of said full-height convolutions is adjacent to one of saidreduced-height convolutions across the width of the turbulizer, andwherein said plurality of full-height convolutions and said plurality ofreduced-height convolutions each extend lengthwise along the length ofthe turbulizer; and such that when the turbulizer is provided in thefluid flow passage, the full-height convolutions are positioned in thefull-height area of the tube with their top surface portions in contactwith the top wall of the tube and with their bottom surface portions incontact with the bottom wall of the tube, and the reduced-heightconvolutions are positioned in the reduced-height area of the tube. 2.The heat exchanger of claim 1, wherein the top surface portions of saidreduced-height convolutions are in contact with the top wall of the tubein said reduced-height area of the fluid flow passage, and/or the bottomsurface portions of said reduced-height convolutions are in contact withthe bottom wall of the tube in said reduced-height area of the fluidflow passage.
 3. The heat exchanger of claim 1, wherein said full-heightarea of the fluid flow passage is located centrally in the flow passageand said reduced-height area of said fluid flow passage is located at anedge of the flow passage, adjacent to said full-height area; and whereinthe plurality of reduced-height convolutions of the turbulizer extendaxially along an edge of the turbulizer, and wherein the plurality ofreduced-height convolutions is adjacent to said plurality of full-heightconvolutions.
 4. The heat exchanger of claim 1, wherein the heatexchange tube comprises a pair of plates which are joined together attheir edges and have spaced-apart central portions, wherein said topwall of the tube is provided by one of said plates and the bottom wallof the tube is provided by the other of said plates, and wherein thefluid flow passage is located between the central portions of theplates.
 5. The heat exchanger of claim 1, wherein the reduced-heightarea is located between opposite edges of the flow passage, and spacedtherefrom, and said full-height area is located adjacent to saidreduced-height area; and wherein the plurality of reduced-heightconvolutions is spaced from opposite axial edges of the turbulizer, andthe plurality of full-height convolutions is adjacent to the pluralityof reduced-height convolutions.
 6. The heat exchanger of claim 1,wherein the reduced-height convolutions have a reduced pitch relative tothe full-height convolutions, such that the top surface portions of thereduced-height convolutions are narrower than the top surface portionsof the full-height convolutions, and/or the bottom surface portions ofthe reduced-height convolutions are narrower than the bottom surfaceportions of the full-height convolutions.
 7. The heat exchanger of claim1, wherein the top surface portions of the convolutions in each said roware substantially aligned with the bottom surface portions of theconvolutions in an adjacent one of said rows.
 8. The heat exchanger ofclaim 1, wherein the rows of the turbulizer extend across the width ofthe turbulizer and transverse to the fluid flow axis, such that theconvolutions define openings facing in a direction which is parallel tothe fluid flow axis.
 9. The heat exchanger of claim 8, said full-heightconvolution and said reduced-height convolution which are locatedadjacent to one another across the width of the turbulizer are connectedtogether by a top surface portion or a bottom surface portion of saidfull-height convolution.
 10. The heat exchanger of claim 8, wherein eachof the rows of the turbulizer includes at least one of said full-heightconvolutions and at least one of said reduced-height convolutions. 11.The heat exchanger of claim 8, wherein the turbulizer comprises anoffset strip fin.
 12. The heat exchanger of claim 8, wherein the topsurface portions and the bottom surface portions of both the full-heightconvolutions and the reduced-height convolutions are flat andsubstantially parallel to the top and bottom walls of the tube.
 13. Theheat exchanger of claim 1, wherein the rows of the turbulizer extendalong the length of the turbulizer and parallel to the fluid flow axis,such that the convolutions define openings facing in a direction whichis transverse to the fluid flow axis.
 14. The heat exchanger of claim13, wherein said turbulizer comprises at least one of said rows in whichall of the convolutions are said reduced-height convolutions, and atleast one of said rows in which all of the convolutions are saidfull-height convolutions.
 15. The heat exchanger of claim 14, whereinsaid at least one row of reduced-height convolutions is adjacent to saidat least one row of full-height convolutions.
 16. The heat exchanger ofclaim 13, wherein the top surface portions and the bottom surfaceportions of the reduced-height convolutions are flat and substantiallyparallel to the top and bottom walls of the tube.
 17. The heat exchangerof claim 16, wherein the top surface portions and the bottom surfaceportions of the full-height convolutions are rounded.
 18. The heatexchanger of claim 13, wherein the turbulizer comprises an offset stripfin.
 19. The heat exchanger of claim 18, wherein the side portions ofthe convolutions are interrupted approximately at their midpoints byshoulders through which adjacent rows of said turbulizer are connectedtogether.